Former Prince George's County State's Attorney Glenn F. Ivey filed the paperwork Thursday required to challenge incumbent Rep. Donna F. Edwards, setting up what is likely to be one of Maryland's most competitive Democratic primaries next year.

Ivey, 50, won countywide elections in Prince George's in 2002 and 2006 by wide margins. He will be a formidable challenger in the 4th District, which now includes a large swath of central Anne Arundel County. Ivey has been in private practice since leaving the state's attorney's office in January.

Ivey's decision to take on Edwards comes after the General Assembly and Gov. Martin O'Malley approved a new congressional map last month as part of the state's once-a-decade redistricting. Edwards publicly objected to the new boundaries of the 4th District but lost her fight to change them.

"During tough times, we need to turn to each other and not on each other to provide the best possible representation in Congress," Ivey said in a statement, an apparent reference to Edward's criticism of the new map. "I will be a team player."

A campaign spokesman for Edwards declined to comment.

Ivey filed paperwork with the Federal Election Commission required of any federal candidate who raises or spends more than $5,000 in campaign cash. The race could prove expensive for both candidates, particularly given the high price of running television advertisements on Washington television stations.

In her most recent campaign finance filing covering the past three months Edwards reported raising $69,400 and having $67,031 in the bank.

But Edwards, who has worked to position herself as a progressive voice on national issues, will have support from outside groups. For instance, the Democratic Congressional Campaign Committee, the campaign arm of House Democrats, will support Edwards, said spokesman Josh Schwerin.

The 4th District used to include a portion of Montgomery County.Edwards attacked the new map for leaving Montgomery County minorities without African-American representation in Congress, though her critics suggested she was also concerned about a primary challenge from a high-profile political figure such as Ivey.

Edwards — first elected in a special election in 2008 to fill the vacancy caused by the resignation of Al Wynn — is now in her third term. She is 53.

Matt Verghese, political director for the Maryland Democratic Party, declined to comment on the race, noting that state and national parties generally do not take sides in a primary contest. Verghese denied speculation that party officials will back Ivey because of Edwards' stance against the Democratic redistricting plan.

He called Edwards an "outstanding" congresswoman.

The seat is considered a safe bet for whichever Democratic candidate wins the state's April 3 primary. Nearly 78 percent of the district's voters selected Barack Obama for president in 2008 and 71 percent picked O'Malley for governor last year. Those are high numbers, even for blue-leaning Maryland.

A third Democrat, Anne Arundel County Council member Jamie Benoit, whose council district includes Laurel, said last month that he has formed an exploratory committee to look into a possible run.